When combined with a curing agent, epoxy resins give cured products having a three-dimensionally crosslinked structure and thus exhibiting various desirable characteristics. Crosslinked epoxy groups are exploited in a wide range of applications, such as paints, electrics/electronics, civil engineering/building, adhesives, and composite materials, owing to excellence in the balance between heat resistance and mechanical/physical properties and in electrical characteristics, adhesive characteristics and corrosion resistance, among others, and to the ease of molding.
On the other hand, epoxy resins are generally hard and brittle by nature and may form cracks upon exposure to stress strain or thermal shock on the occasion of curing or in use, hence epoxy resins are required to be rendered tenacious and flexible. In the field of IC sealing, for instance, where packages are becoming smaller and thinner, improvement in crack resistance is needed.
As a means for providing epoxy resins with flexibility, there may be mentioned the combined use of a flexible epoxy resin. The flexible epoxy resin includes, among others, diglycidyl esters of long-chain fatty acids such as linoleic acid dimer; polyglycidyl ethers of polyhydric alcohols such as glycerol, pentaerythritol and trimethylolpropane; diglycidyl ethers of polyalkylene glycols such as polyethylene glycol; and the like. However, long-chain fatty acid glycidyl esters are short of alkali resistance and gasoline resistance, although they are excellent in flexibility. Polyalkylene glycol glycidyl ethers also have problems, for example they are inferior in weathering resistance.
It is known that crosslinking functional group-terminated liquid oligomers, when used alone or combined with an appropriate curing agent, give cured products excellent in rubber elasticity. Thus, it is expected that an epoxy-terminated vinyl polymer, if successfully obtained in a simple and easy manner, might serve as a novel flexible epoxy resin excellent in flexibility. Further, vinyl polymers show various characteristics depending on the main chain skeleton thereof and, therefore, are amenable to molecular design according to the use/purpose thereof.
As for the production of epoxy-terminated vinyl polymers, U.S. Pat. No. 4,429,099, for instance, discloses a method which comprises reacting the termini of polyisobutylene with a phenol in the manner of Friedel-Crafts reaction and further utilizing the reactivity of the phenol group to synthesize an epoxy-terminated polyisobutylene. However, low-polarity polymers such as polyisobutylene are poor in compatibility with epoxy resins and, if well dispersed, give a high viscosity.
In view of the above state of the art, it is an object of the present invention to provide a vinyl polymer with an epoxy group terminally introduced therein and an epoxy resin composition in which such polymer is used.
A further object of the invention is to provide an epoxy resin composition having flexibility by adding a vinyl polymer having a terminal reactive functional group to an epoxy resin.